Apparatus for the pneumatic separation of materials of different specific gravities and sizes



2,141,451 APPARATUS FOR THE PNEUMATIC SEPARATION OF MATERIALS Dec. 27,1938. F. F. RIDLEY OF DIFFERENT SPECIFIC GRAVITIES AND SIZESZYSheetS-Sheet 1 Filed June 1, 1936 2,141,451 APPARATUS FOR THEPNEUMATIC SEPARATION OF= MATERIALS Dec. 27, 1938. F. F. RIDLEY OFDIFFERENT SPECIFIC GRAVITIES AND SIZES 2 sheets -she t 2 Filed June 1,1936 Patented Dec. 27, 1938 UNITED STATE 3 PAT EN'T OFFICE APPARATUS FORTHE PNEUMATIC? SEPA- RATION or MATERIALS OF DIFFERENT! sPEomIcGRAWIT-IES- AND SIZES/ Frank Frost Ridley, Rutland Park, Shefl'ield,

England, assi'gnor to Colliery Engineering Limit'ed, Yorkshire, England,a British joint-stock company Application June 1, 1936, Serial No.82,998 InGreat Britain June- 5, 1935 6 Claims. (01. 209-44) Thisinvention comprises improvements in apparatus for the'pn'euma'tic'separation ofmaterials ofdifferent specific gravities and sizes, such'10 of separating such materials according to Patent No. 1,843,405 issuedto George Raw on February 2,.1932, which relates to the use of staticpneumatic pressure to achieve stratification between materials ofdifferent densities, but without regard to the sizes of the particles.This latter process is of particular usefulness in the treatment offines, because it eliminatespre-sizing, which is especially difficultandtroublesome in the finer sizes.

The separate pneumatic treatment of very fine sizes, as compared withthe'larger material such as up to 1" or 2",. has presented difficultiesmainly owing to the muchslower rate of stratification and the greatersensitiven'ess of the bed of. materials to the pneumatic conditionsapplied to it. The slower rate of I stratification of fine materialsmakes it desirabletooperateon a relatively thin bed of materials and'also to provide a considerable length of table over which the materialshave to pass and thus a considerable period of treatment, inorder toensure efficient purification. However, the greater sensitiveness of thebed whenworki'ng with thin beds of fine materials, for example beds from1" to 2" thick, imposes conditions of delicacy requiring accuratecontrol in order to maintain, during the full period of stratification,the proper condition of balance and fluidity which is necessary'forstratification in the bed ofmaterials. 40 As aresult, it is foundthat there are practical limits to the length and areaof bed which canbe separately maintained in the properand uniform condition required forstratification. If it is attempted to work with too great'an area, it isfound that, owing to inevitable variations in character of thematerials, one part: of the bed may be liable toburstunder the influenceof the pneumatic pressure and destroy stratification which has alreadytaken place.

In dry cleaning tables, the stratification'of the materials and theseparation of the layers one from another usually proceed concurrentlyand, in many cases, certain quantities'of' the coal or other less densematerial are discharged progressively. as they become freed of thedenser It is also of particular utility in carrying out the processmaterial or impurities, whilethe latter, such as concentrated shale orstone, progresses to the end of the table. However, with fine materials,owing to the slower stratification, this does not provide the bestopportunities of completely puri- 5v fying the coal. It is better toarrange for the coal or the like to pass over asnearly as possible thewhole length of the table before discharge, thus subjecting it to-thecleaning influence for the maximum'period. 10-

In some dry coal cleaning tables,- attempts have been made to secure theadvantage of this long treatment byemploying variousmeans for extractingthe stratified shales through the deck or table surface and allowing thecoal to passon 15 to the end, but difficulties have usually beenassociated with these discharge means. In the first place, it hasbeen'found that the fluid condition of a bedof' fine materials-on a longtable ordeck causes it to assume different thicknesses. This 20disturbance of the conditions of the bed upsets the stratificationsothat it is diflicult to obtain effective discharge of theshale. In thesecond place; if' the lower stratum bedischarged' directly from a slotdevice disposed transversely of- 25 the table, a large area will beprovided suflicient for the undesired discharge of coal with shale. Inadditionpneumaticpressureis-liable to escape violently through the slotinstead of going through the bed: If, in order to avoid these de- 30fects, the slot be connected'with a shale chute having intermittentlyoperated means for discharging shale, the bed isdisturbed by theintermittent action ofsuch means.- Alternately if the escape ofair isavoided by disposing the slot 35 in animpervious part of the table theportion of the bed in the neighbourhood of the slot is unsupported bypneumatic pressure and the bed will notice maintained in the desiredfluid condition.

Finally, means fo'rshaving off :the' lower stratum 40,

anddischa'rgingit througha slot are liable'to-disadvantages owing to thefact that the shaleoccu pies'only a" relatively thin" layergand theirregular shape of the particles-produces an ill-defined line ofdemarcation between thestrata 45 The principal object of the presentinvention is to provide an iii'iprov'ed construction: for the efficientseparation of fine materials on a" long table, while avoiding:undesirable fluctuations" in thickness of the bed and providing for thedis- 50 charge of the bottom: layer in such a manner as toprevent unduedisturbance of the fluidconditions-ofthe-bed; I I V According-to thisinvention atable on deck dis-- posed over an air box: is dividedlntoa=number of 55 stratifying ones by transverse slopes or steps, and

discharge of the lower stratum of materials is effected in a restrainedmanner, so as not to disturb the fluid conditions of the bed, by sieves,in the table disposed at the forward end of the zones. The division ofthe table by the slopes enables zones of predetermined area to beprovided for ensuring proper control of the stratification conditionsand for avoiding irregularities in the bed; Thus the table is dividedinto a number of zones or areas of a size not too large for propercontrol of the conditions, and before any irregularity is able to occurthe stratification in one zone is completed, a part of the shale isdischarged and the bed is re-formed for further treatment in the nextzone. The coal is thereby subjected to a prolonged treatment in thesucceeding zones and the shale is discharged without I disturbing theconditions in the bed. In the ab. sence of the slopes, the fluidity ofthe bed would cause it to run away at some points and build up atothers; The re-formation of the bed in succeeding zones avoids thisdisadvantage.

The sieves are adapted for an effective discharge of the shale whilepreserving the uniform fluid conditions. The pneumatic pressure is ableto pass through such sieves at all times owing to the disposition of thetable over a single air box. The sieves are suitably provided by narrowtransverse portions having perforations considerably larger than thosein the deck and slightly larger than. the size-of the, largest particlestreated. These sieves enable the shale to be discharged in a restrainedmanner without in any waydisturbing the conditions of the bed, theeffect being to allow the lower surface ofithe shale layer to bedischarged, in contradistinction to the discharge of the whole of alower layer as in the case of an uncontrolled slot discharge.

In order to enable the invention to be readily understood reference willbe made to the accompanying drawings, illustrating by Way of example,different constructions of apparatus for carrying the invention intoeffect, in-which draw:

1ngst Figure 1 is a side elevation with parts in section of oneconstruction of apparatus in which the table is provided with sieves fordischarge of the shale.

Figure 2 is a plan of Figure 1, with the dust hooding over the tableremoved.

Figure 3 is a section, to an enlarged scale, on the line III-III, Figure2. V. Figure 4 is a section, to an enlarged scale, on the line IV-IV,Figure 2.

Figure 5 is a diagrammatic view construction.

of a modified Figure 6 is a plan view of the forward end of a modifiedconstruction of table, and V V Figure '7 is a centrallongitudinalsection of Figure 6. f

Referring to Figures 1 to 4, the apparatus comprises a rectangular tablea of trough form with a perforate deck I), and upstanding sides 0 tomaintain a given thickness of. bed. The deck is divided into a number ofstratifying zones or cells A, B, C, arranged at .difierent relativelevels,

each one being lower than the one preceding it. The forward end of onezone is connected with the rearward end of the next zone by an im- 1through; the remaining sieves.

connected to any suitable conventional vibrating mechanism to give'asmall throw at high periodicity. The table is slightly declined from thefeed end a to the discharge end a to secure progression of the materialsby gravitational flow. Other vibrating mechanisms can be applied asalternatives, and if they provide a component which causes forwardprogression of the materials, the forward declination of the table willnaturally be decreased. Pneumatic pressure is supplied by a fan 71.through the duct 1' and pulsator 7 to the air box It. Aflexibleconnection k is provided between the table and the air box. Dust hooding1 maybe provided over the table, any suitable means being employed forseparating or settling the dust. The manner of supplying the pneumaticpressure isdescribed and shown in patents issued to George Raw: No.1,730,947, dated October, 1929; No. 1,811,026, datedJune 23, 1931; andN0. 1,843,405, dated February 2, 1932. V

In operation, the raw materials such as coal fed tothe table at a flowsin the manner of a liquid, under the influence of vibration andpneumatic pressure, the shale or the like gradually stratifying at thebottom of the bed. At the end of the'firstzone A, a certain amount ofStratified shale has collected at the bottom of the bed, and thisriddles through the sieve e. The partially cleaned coal or the likeflows down the imperforate slope d and issubjected to furtherstratifying action in the next zone B, further shale or stone beingdischarged through the sieve of this zone. The treatment proceedssimilarly in the next zone. 7

By dividing the deck into several zones or compartments with'imperforate slopes between them, the tableis divided into a'number ofstratrestrained discharge action to be obtained, only part of the layerof shale beingpassed through any particular sieve. Only a thin stratumof the lower layer is discharged through any particular sieve. Aprotective layer of shale may thus be provided between the coal and thedischarged shale, so as to prevent mixing and loss of coal in the shale.The, present invention provides a'progressive discharge'of shalethe'heaviest and most easily'stratified passing through'the first sieves and progressively lighter shale passing In order to en-' suredischarge of completely clean coal at the forward end of the table, somecoal may be allowed to beldischarged with'the last vestiges of shalepassing through the final sieve; The prodnot passing through thisparticular sieve would be principally middlings and could be extractedfrom the air box -]c by independent discharge means and re-fed to thetable f rre-treatment with the raw'material. Sucha re-feeding willusually provide sufiicient' margin tocompensate for variations in thequantity of. shale in the raw feed. If desired, however, a further ad'-J'ustment may be provided by arranging for one or more of the sieves tobe put out of action by plates having perforations of the same size asthe perforations in the main deck. For example as shown in Figure 3closure plates m may be fitted under the table a on hinges n so that theplate can be swung clear of the sieve e (as shown in dotted lines) by alever device 11. on the side of the table. The plates m can-be swungupwards to obstruct the sieves when desired.

Instead of allowing the coal to be discharged directly from thestratifying zone C, while the.

middlings and remnant of coal are discharged through the sieve; e, theparticular arrangement illustrated may be adopted. In this arrangementprovision is made for a. sharper final separation between-the lastportion of stone extracted and the middlings which would otherwise passinto the air box k withthe stone. Thus over the imperforate slope d ofvthe last zone there may be disposed a skimmer. or cutter. o. Thisskimmer, which may be vertically adjustable, divides the strata of thebed, middlings passing underneath the skimmer being diverted. bydeflectors 0 into a central channel p having a perforated bottom. Abovethe skimmer plate 0 are provided deflectors 0 which divert the coalflowing over. the plate into side channels disposed alongside thecentral middlings channel 1). The bottoms of the coal channels 29 arenormally blank, but may be provided with perforations if. desiredtopermit of the air passing throughthe material to assist its passage tothe end of the table. When perforated. a. further. cleaning; may takeplace in these channels, which are then provided with discharge slots attheir forward ends to discharge any last vestiges of. impurities. Suchmaterial discharged throughtheslots would. contain coal and would bepassed into the middlings for retreatment. The slots in this case wouldbe beyond the end of the air box so that the material can be passedintothe main middlings chute.

In the channel p the middlings are subjected to a further stratifyingaction. A second coal skimmer plate q. is provided at the end of thechannel, the deflectors q diverting coal into the sidechannels 11 whilethe middlings pass underneaththe plate into. a short zone 1'. The cleancoal is discharged from the channels 10 into chutes s. As shown inFigure 4 the zone 1 is extendedv a short distance beyond the end of theair box is to allow the middlings to discharge into a middlings chute 1beyond the clean coal. If the bed weretoo sluggish however a smallextension such as a pipe and a small box, connected to the air box couldbe provided for supplying air pressure also to the forward portion ofthe zone 1. A skimmer plate t is provided at the forward end of thezone 1. Shale passes under this skimmer to a discharge outlet u, whilethe upper stratum of middlings passing over the skimmer is divertedlaterally by deflectors A flap device '0 directs the middlings eitherinto the outlet r so that they may be re-fed to the table, or into theoutlet s for theclean coal. The two positions of the flap device, whichis adjustable by a handle 0 are-shown in dotted lines, Figures 1 and4.

In order to maintain even thickness of bed in the zones, small-dams 10,Figure 4 may be fitted just: forwardly: of thesievese andiacross. the.full 7 width of the deck for-retaining the bed at given thickness.These damsare, as shown, only veryshort, as the thin beds have verylittle tendency to minor break away as they pass. over the slopesbetween the cells. The dams must not be too deep or they would tend tocause the bed to pile up and thicken and thereby destroy the regularityof the bed conditions. The dam may alternatively be in.the form of ablade 1:, Figure 3, which also serves for maintaining separation of thelayers after discharge of impurities through the sieve e. The blade isdisposed horizontally above the sieve and is connected to a somewhatwider blade m disposed above the slope d at approximately the sameinclination. One or both of the blades :11, :1: may be adjustable forvarying their inclinations. The horizontal blade at serves to dam theforward flow of materials and thereby maintain an even thickness of bed,while the inclined portion 90 serves to preserve on the next zone theStratification obtained in the preceding zone, since it will be realizedfrom Figure 3 that the denser materials flow under the blade and theless dense materials flow over it.

The shale discharged through the sieves e falls into the air box k,Figure 1, and may be extracted therefrom by any suitable meansincorporating an air-sealed discharge. For example, the shale may bedischarged into a small enclosed hopper y fitted with a balance valve yat the bottom to retain a given level of material inthe hopper. A screwconveyor 2 disposed along the bottom of the air box feeds the shale intothe hopper.

According to the modified arrangement shown in Figure 5 the tablecomprises three stratifying zones, although four or more may beemployed, each zone having a sieve discharge at its forward end. In thisarrangement shale or the like discharged through the sieves l8 fallsthrough the air box 70 and is discharged from hoppers l9 formed in thebottom of the box beneath the sieves. Middlings fall from the finalsieve is through the air box to a third hopper I9 The hoppers are fittedwith automatic discharge valves I So under constant air-lock conditions,conveyors being disposed beneath the hoppers for carrying the materialaway. Clean coal flows over the forward end of the table to discharge.Additional hoppers would be provided in accordance with the number andposition of the bottom discharges provided in the deck.

According to the modified arrangement shown in Figures 6 and '7, theshale and middlings are separated at the end of the central trough orchannel 2| by the adjustable skimmer or cutter 22; The middlings passover the skimmer to a chute 23 and the shale passes beneath to anotherchute 24. The two chutes 23, 24 are in line with the central channel 2!just beyond the air box.

In normal circumstances, the sides of the table are parallel and ofconstant width, but under some conditions it may be found desirableslightly to vary the widths of the cells. The purpose of this is toaccommodate variations in the rate of flow of materials, which sometimesis liable to occur with fine material of the kind in question, and maybe caused partly by the removal of shale. Variations in width, however,are only slight, and may be suitably provided for by fitting strips ordistance pieces to the insides of the walls of any particular section.Suchvariations in the widths of the cells are not for the purpose ofvarying the thickness of the bed but for the purpose: of maintaining it.atzuniform thickness when a tendency to thinning might otherwise occur,due to an increased rate of fiow at one portion.

It will be seen that the whole object is to make practically the wholelength of table available for cleaning the coal, while at the same timeextracting the shale progressively as it becomes stratified, and withoutin any way'interfering with the conditions of stratification. The sievesdo not cause any tendency for the air pressure to be violent at thesepoints, becausethe discharge is restrained and the stratified shale liesin a heavy bed upon them and prevents any such free flow of air. Also,when working under the static pressure condition, the size of dischargeslots or perforations has very little effect, because the quantity ofair flowing is negligible.

The improved tables are of particular advantage incarrylng out thestatic pressure process of separation already referred to. They may beoperated singly orin multiple or pairs. Two or more tables may bearranged side'by side on one frame'or chassis and provided with a commonair box or chamber or separate air chambers or each of severalseparating units may comprise multiple tables side by side, for examplein the manner described in patent application Serial No. 643,258 nowPatent No. 2,100,670, issuedto George Raw on November 30, 1937. One fanmay be used to serve several tables or to serve several units eachcomprising several "tables, connection betweenithe fan and the air boxesor chambers being by branched pipes or otherwise and the pulsators ofthe several tables being set so as to give sequential pulsations throughthe several air boxes or chambers, where necessary, to' preserve uniformload on the fan,

as in Patent No. 2,100,670 above noted. In the case of tables placed inmultiple side by side on' a single chassis, the invention'provides theadvantage that all the less-dense materials are discharged at theforward end of the chassis and no side discharges are necessary. Thisenables the two or more tables or decks to be built adjacently and closetogether andonly a partition ora single side wall need be used to divideone deck from another. As large a table as desired, within mechanicallimits, can thus be built without departing from the best size'of alwaysbeen found the most difficult material to treat on pneumatic drycleaning tables.-

I claim:

1. Apparatus for the separation of materials of different specificgravities by stratification of the materials due to pneumatic pressure,comprising an air box, a table having a pervious bottom disposed oversaid air box, a number of impervious slopes extending transversely ofthe table to provide a number of stratifying zones at different levels,sieves "for the discharge of the lower stratified layer disposedinthepervi'- ous bottom at the forward'end of each zone, and controllablemeans adjustable for shutting off discharge through said sieves. J a

2. Apparatus'for the separation of materials of different specificgravities by stratification of the materials dueito pneumatic pressure,comprising an air box a table having a pervious bottom, disposedover'said airbox; a number of.

impervious slopes'extending transversely of the table 'to provide anumber of stratifying zones at different levels, narrow sieves for thedis-' charge of the lower stratified layer disposed in the perviousbottom at the forwardend of each zone and having perforations largerthan those in said bottom, closure plates having perforationsapproximating to the size of those in the bottom, and means foradjusting said plates for obstructing the discharge of materials throughsaid sieves into the air box. 7

3. Apparatus in accordance with claim 2, comprising pivotally mountedclosure plates and handles external of the air box for adjusting saidplates; A v

4 Apparatus for the separation of materials of different specificgravities by stratification of the materials, comprising an air box, atable disposed over said air box and having a stratification zone with afiat pervious bottom, means for maintaining a bed of materials ofsubstantially even thickness on said zone, means for subjecting the bedto the influence of static pneumatic pressure for -maintaining the bedas a whole in 'equilibriumwith said pressure to inducea state offluidity in the bed with the minimum escape of air therethrough and'anarrow discharge sieve disposed in the pervious bottom across 'thewidthof the table at the for- 5 ward end of the stratifying zone, said sievebeing in pneumatic communication with the air box and havingperforations larger than those in the pervious bottom and at least aslarge as the. largest particles of the lower stratified layer ofmaterials for riddling the lower layer into the air box at the end ofthe stratifying zone while the less dense materials stratified. by' saidpneumatic pressure occupy the upper layer, due to the maintenance of the'fiuid conditions above the said sieves during the dischargetherethrough of' material from the lower stratified layer.

. 5,Apparatus for the separation of materials of different specificgravities by stratification of the materials, comprising pneumaticchamber apparatus, a table having a pervious bottom disposed over saidpneumatic chamber apparatus, impervious slopes disposed at intervalstransversely of the table to divide it into'a num-. ber of stratifyingzones at successively lower levels the farther they. are disposed awayfrom the feed end of the table, means on said table for maintaining abed of materials of substantially even'thickness thereon, means forsubjecting the bed to the influenceo'f static pneumatic pressure'formaintaining the bed as a whole in equilibrium with said pressure toinduce a state of fluidity in the bed with theminimum escape of airtherethrough and a narrow discharge sieve disposed in the perviousbottom across the width .of the-table at the forwardend of eachstratifying zone, said sieve being in pneumatic communication' with saidpneumatic chamber appa ratus and having perforations larger than thosein the perviou's'b'ottom and at least as largeas the largest particlesof the lower stratified layer for theiriddling of the lower layer intothe pneumatic chamber apparatus at the completion of "the'stratificationin each zone while the less dense materials stratified by said pneumaticpressure. occupy. the upper layer, due to the' V maintenance of "thefluid conditions, above the said sieves during. the dischargetherethrough of material from'the lower stratified layer.

r 6. Apparatus :for the separation 'of .materials of difierent specificgravities by stratification of the materials due topneumatic pressure,comprising an air box, a table having a pervious bottom disposed oversaid air box, imprevious slopes disposed at intervals transversely ofthe table to divide it into a number of stratifying zones atsuccessively lower levels away from the feed end of the table, means onsaid table for maintaining a bed of materials of substantially eventhickness thereon, a narrow discharge sieve disposed in the perviousbottom across the width of the table at the forward end of eachstratifying zone, said sieve continuously allowing the application ofpneumatic pressure to material over it and having perforations largerthan those in the pervious bottom and at least as large as the largestparticles of the lower stratified layer for the riddling of the lowerlayer into the air box at the completion of stratification in each zone,blades disposed over said sieves for dammin-g the flow of materials overthe table and blades disposed over the slopes at approximately the sameinclination for preserving in the next zone the Stratification obtainedin the preceding zone. 1

FRANK FROST RIDLEY.

